Geological Circumstances Behind Washington Mudslide

As search efforts intensify around the site of Washington state's devastating mudslide, geologists are looking into causes of the rapid collapse of the 1,500-foot-wide segment of hillside in Snohomish County that suddenly cut away and crushed the homes and roads below.

The chief culprit appears to have been the glacial composition of the hillside, which is made of silt, clay and soil, and very little rock, which tends to be very loose.

When these collapse they create something called a "rotational slide," meaning that the land turns on itself, with the base of the hills moving upward as the top collapses.

David Montgomery, a geologist at University of Washington explains the geological circumstances behind the mudslide.